Boeing chief speaks of 'tragic loss' as prosecutors investigate 737 Max planes

The chief executive of Boeing on Monday night broke company leadership’s near silence over two recent crashes involving the 737 Max aircraft type, as US federal prosecutors and regulators opened an inquiry into the plane’s development process.

Dennis Muilenburg issued statements in writing and via video and said: “The tragic losses of the Ethiopian Airlines and Lion Air flights affect us all and we join the world with heavy hearts in grieving.”

Muilenburg extended “our deepest sympathies” to the families and loved ones of those who died on Ethiopian Airlines flight 302, which crashed last week with the loss of all onboard.

He said the US manufacturer was cooperating with investigating authorities and said “the investigation is moving forward”.

US federal prosecutors and regulators opened an inquiry into the development of Boeing 737 Max airplanes following the two fatal crashes, a move that came as scrutiny is mounting over Boeing and the US’s top aviation regulator’s role in certifying the aircraft.

Related: Ethiopian Airlines flight data has 'clear similarities' with Indonesia crash

The Department of Transportation inquiry, issued by grand jury in Washington DC on 11 March and first reported by the Wall Street Journal, includes an unusual subpoena from the justice department’s criminal division seeking documents, including correspondence, emails and other messages related to the 737 Max’s development.

The investigation comes days after the Federal Aviation Administration (FAA) grounded 737 Max planes indefinitely following the Ethiopian Airlines disaster earlier this month, which came less than five months after a Lion Air 737 Max crashed in Indonesia, killing everyone onboard.

The justice department investigation will focus on the Lion Air accident and the role of the plane’s automatic anti-stall safety system. The loss of the Ethiopian plane is not so far included, despite apparent similarities between the two accidents highlighted by the Ethiopian minister of transport over the weekend.

On Monday night, Muilenburg’s statement said the company was cooperating fully with the FAA, the Department of Transportation and the National Transportation Safety Board. And he sought to reassure the flying public over the safety of the aircraft type.

“Soon we will release a software update for the 737 Max that will address concerns discovered in the aftermath of the Lion Air Flight 610 accident,” he said.

Boeing experts are now at the crash site in Africa where the subsequent Ethiopian Airlines flight went down, “to share technical expertise”, Muilenburg said.

“The depth of pain felt by the loved ones of the passengers and crew onboard is difficult to fathom,” he said.

Promising “excellence and integrity” from the company, Muilenburg added in his statement: “Safety is at the core of who we are at Boeing.”

But the vexed questions about the causes of the crashes persist for investigators, the bereaved and the flying public.

A preliminary report into the Lion Air crash showed that the pilots struggled with an automatic safety system, known as the maneuvering characteristics augmentation system (MCAS), which was designed to activate automatically only in the event of a high-speed stall.

Lion Air’s black box data indicated that a single faulty sensor triggered MCAS multiple times during the brief flight, initiating a tug of war as the system repeatedly pushed the nose of the plane down and the pilots wrestled with the controls to pull it back up.

In grounding the Max last week, the FAA cited similarities in the flight trajectory of the Lion Air flight and the crash of Ethiopian Airlines flight 302.

On Monday, Boeing announced it is working with the FAA to update software related to the MCAS system to make the planes safer. The news came after an alarming Seattle Times report claimed FAA officials pushed engineers to hand off responsibility for the safety of the 737 Max to Boeing itself.

According to engineers who worked on the system, Boeing’s own analysis of the safety system had several crucial flaws, including underestimating the power of the system to control the horizontal tail to push the nose down to avert a stall.

Moreover, the system could move the tail farther than the initial analysis stated and would reset itself each time a pilot responded, repeatedly pushing the airplane’s nose downward.

The system could also be triggered by a single sensor, a failure of which was listed in the analysis as one level below “catastrophic”.

The FAA said it followed its standard certification process on the Max, while Boeing told the paper the regulatory agency had “considered the final configuration and operating parameters of MCAS during Max certification, and concluded that it met all certification and regulatory requirements”.

But according to an engineer contacted by the paper, “there was constant pressure to re-evaluate our initial decisions. And even after we had reassessed it … there was continued discussion by management about delegating even more items down to the Boeing Company.

“There wasn’t a complete and proper review of the documents,” the former engineer added. “Review was rushed to reach certain certification dates.”